1. Field of the Invention
The invention regards a cabling unit for grooved bus bars with T-shaped cavity. The cabling unit of the invention may be used for obtaining connections to grooved bus bars belonging to structures of various types.
Preferably, the cabling unit of the invention is most commonly used in electrical cabinets and switchboards where it is used for connecting electrical devices, such as for example switches, disconnectors or other devices, to the grooved bus bars with a T-shaped cavity for the distribution of the electric power.
2. Present State of the Art
The electric power distribution bus bars that are used in electrical cabinets and switchboards are constituted by shaped elements with longitudinal extension, each of which is provided with a T-shaped groove which traverses it length-wise.
According to the prior art, special screws with hammer head are inserted in the groove for fixing—to the bus bars—the terminals of the electrical cables that supply the different components housed in the switchboard or cabinet, such as for example switches, disconnectors, deviators and other electrical devices. A distribution bus bar of the known type is represented by way of example in FIG. 1, in which it is indicated in its entirety with A.
The bus bar is longitudinally traversed by the groove B, which is accessible through the longitudinal slot C and is configured to receive the screw D having the hammer head D1 provided with an elastic element D2.
When mounting the screw D, the operator holds it by the threaded shank D2, arranges it with the hammer head D1 aligned to the slot C and then inserts it into the groove B, as observable in FIG. 2.
In this configuration, the screw cannot be rotated given that, as observable, the lateral walls of the hammer head D1 counteract the walls of the slot C.
Rotating the screw requires forcing the hammer head D1 against the bottom of the groove B so that the compression of the elastic element D3 allows the hammer head D1 to fully enter into the groove B, as observable in FIG. 3, up to freeing the walls thereof from contact with the walls of the slot C.
In such position, the screw D can be rotated in the clockwise direction until it is arranged transversely to the slot C in the position observable in FIG. 4.
Once the rotation is completed, the screw D is released and the expansion of the elastic element D3 pushes the underhead of the screw D counteracting the inner surface of the groove B so that the screw remains constrained in the position observable in FIG. 5.
Thus, the screw D is self-supporting and the operator does not have to support it during fastening for cabling operations.
The presence of reliefs D4 arranged at the underhead, which counteract the wall of the slot C once the rotation has occurred, limits the amplitude of the rotation angle that can be imparted to the screw to 90° and serves as an end stop which prevents any further rotation of the screw D and guarantees the required reaction for fastening the bolt H.
The use of self-supporting screws with a hammer head has the advantage of facilitating the cabling given that, after insertion thereof into the grooves of the bus bars, they remain in position and the operator can work using both hands.
Various types of self-supporting screws with a hammer head and provided with variously shaped elastic elements are available in the market, but they all reveal the known drawback lying in the fact that after being arranged in the self-supporting operating position in the groove B, an inadvertent counter-rotation in the anticlockwise direction easily returns them to the initial configuration of FIG. 3 in which they can project from the groove B.
As a matter of fact, the elastic element that guarantees the self-support of the screw does not provide—against the bottom of the groove B—a friction sufficient to effectively counteract a counter-rotation torsional moment, which may at times be inadvertently caused by the operator when operating the fastening tools.